Caption: Green fluorescent protein molecule. Computer model showing the secondary structure of a molecule of green fluorescent protein (GFP). Some central atoms are represented as rods. The molecule has a cylindrical structure formed from beta sheets (ribbons). GFP is found in the Pacific jellyfish Aequorea victoria. It fluoresces green when blue light is shone on it. GFP is widely used as a research tool in biology and medicine. The gene coding for it can be tagged to the genes of other proteins or viruses to study their movements within cells. They can also be used to tag cancer cells to track their spread through the body.